Potentiometer devices are sufficiently well known and are implemented for position determination of an element, such as, for example with throttles, exhaust gas feedback valves, etc. Circuit failure detection for short circuits and cable disconnections using a potentiometer is known, as demonstrated by the IC engine throttle valve failure detector described in DE 4020106 C2. In the device taught by this reference, a pull-down resistance or a pull-up resistance is provided in a valuation circuit of a control unit, which provides a voltage signal to an A/D converter as a fail signal. The fail signal is either an implausibly low potential or an implausibly high signal. A potentiometer of this type has the disadvantage in that, even with high so-called “noise resistance” occurring between the sliding track and the sliding element, such as may be due to impurities or friction polymers, for example, an erroneous failure signal may still be produced.
In particular, the danger of high noise resistance arises in the case of exhaust gas feedback valves that can, over long periods of time, be used in an offset region, and correspondingly are locked continuously over a relatively long period of time. Consequently, the sliding element is not moved over the sliding track for this extended period. This inactivity often leads to an undesirable erroneous fail signal due to operation of the valve in the offset region. An erroneous fail signal is one that is not relevant to emission or diagnosis operations related to the exhaust gas feedback valve. One solution to the problem of erroneous fail signals is described in the DE 4020106 C2 reference, wherein noise peaks in the output signal of the potentiometer are suppressed as much as possible. However, this solution is cost intensive to implement because differing potential states for the control unit are required.
One object of the present invention is therefore to provide a potentiometer device that simply avoids an erroneous output signal due to noise resistance in the offset range.
Another object of the present invention is to provide a potentiometer device that is inexpensive to implement and avoids erroneous output signals while operating in the offset range.
Another object of the present invention is to provide a potentiometer device that avoids erroneous output signals while operating in the offset range and that can be connected to a control unit that has a single potential state rather than requiring connection to a control unit having differing potential states.
Another object of the present invention is to overcome the disadvantages of the prior art potentiometer devices while retaining the advantages of these devices.